An undated image shows Omar Mateen, who authorities say killed lots of individuals within the Pulse nightclub in Orlando, Fla., on Sunday. Myspace/via AP hide caption

Omar Mateen, whom authorities say killed 49 individuals during the gay nightclub Pulse in Orlando, Fla., had been apparently no stranger into the club.

Multiple news outlets are reporting that some Pulse regulars respected Mateen, stating that he had invested time during the nightclub prior to the shooting early Sunday. Witnesses have actually stated similar to authorities, NPR's Dina Temple-Raston reports, citing U.S.